Re: [Xen-devel] [PATCH 09/14] livepatch: Add per-function applied/reverted state tracking marker

From: Julien Grall <julien.grall@arm.com>
To: "Wieczorkiewicz, Pawel" <wipawel@amazon.de>
Cc: "Tim Deegan" <tim@xen.org>,
	"Stefano Stabellini" <sstabellini@kernel.org>,
	"Wei Liu" <wl@xen.org>,
	"Konrad Rzeszutek Wilk" <konrad.wilk@oracle.com>,
	"George Dunlap" <George.Dunlap@eu.citrix.com>,
	"Andrew Cooper" <andrew.cooper3@citrix.com>,
	"Ian Jackson" <ian.jackson@eu.citrix.com>,
	xen-devel <xen-devel@lists.xen.org>,
	"Pohlack, Martin" <mpohlack@amazon.de>,
	"Ross Lagerwall" <ross.lagerwall@citrix.com>,
	"Jan Beulich" <jbeulich@suse.com>,
	xen-devel <xen-devel@lists.xenproject.org>,
	"Roger Pau Monné" <roger.pau@citrix.com>
Subject: Re: [Xen-devel] [PATCH 09/14] livepatch: Add per-function applied/reverted state tracking marker
Date: Thu, 22 Aug 2019 11:43:19 +0100	[thread overview]
Message-ID: <24f7f2f0-13f3-58e1-0891-921b5048d939@arm.com> (raw)
In-Reply-To: <485AB113-81CD-4700-8A29-F2939F125EA6@amazon.com>

Hi,

On 22/08/2019 11:20, Wieczorkiewicz, Pawel wrote:
>> On 22. Aug 2019, at 12:07, Julien Grall <julien.grall@arm.com 
>> <mailto:julien.grall@arm.com>> wrote:
>> On 22/08/2019 08:44, Wieczorkiewicz, Pawel wrote:
>>>>> diff --git a/xen/include/xen/livepatch.h b/xen/include/xen/livepatch.h
>>>>> index 2aec532ee2..a93126f631 100644
>>>>> --- a/xen/include/xen/livepatch.h
>>>>> +++ b/xen/include/xen/livepatch.h
>>>>> @@ -117,7 +117,7 @@ int arch_livepatch_quiesce(void);
>>>>>  void arch_livepatch_revive(void);
>>>>>    void arch_livepatch_apply(struct livepatch_func *func);
>>>>> -void arch_livepatch_revert(const struct livepatch_func *func);
>>>>> +void arch_livepatch_revert(struct livepatch_func *func);
>>>>
>>>> I doubt livepatch on Arm will compile after this change.
>>>>
>>> What would be you suggestion then?
>>
>> Cross-compiler are nowadays widely available. So build testing your changes in 
>> common code would be the minimum.
>>
> 
> I wish it was that simple. Nevertheless, I will try to prepare an environment to 
> perform such builds.

Cross-compiling the hypervisor is really easy ;).

1) Download the cross-compiler tarball (here one [1]) and uncompress it. You can 
also install the one provided by your distro.

2) Build Xen hypervisor. Here an example for arm64:

42sh> cd xen.git/xen
42sh> make XEN_TARGET_ARCH=arm64 CROSS_COMPILER=<triplet>-

In my case, I am using the Arm toolchain AArch64 GNU/Linux target 
(aarch64-linux-gnu). So the <triplet> would be aarch64-linux-gnu.

This is assuming you have the compilers binary in your PATH. If not, you can use 
give the full path:

CROSS_COMPILER=/opt/gcc-arm-8.3-2019.03-x86_64-aarch64-linux-gnu/bin/aarch64-linux-gnu-

> 
>> In this case, as you dropped the const from the prototype, you will need to do 
>> the same in the declaration.
>>
> 
> Yes, but I see 2 options here:
> - Enable the feature also for Arm (I prefer that, but will not be able to test 
> that in nearest future)

I think some of the code can be made common. So we could possibly rely on x86 
for that. Additionally, IIRC, Konrad has a setup on the cubietruck for testing 
livepatch.

> - Keep Arm excluded and sprinkle code with #ifdef CONFIG_X86

Please no #ifdef CONFIG_X86 in the common code. If you don't plan to support 
Arm, then we should introduce a new Kconfig that will gate all those changes.

Cheers,

[1] 
https://developer.arm.com/tools-and-software/open-source-software/developer-tools/gnu-toolchain/gnu-a/downloads

-- 
Julien Grall

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